Ink jet printing systems enable reductions in noise and running costs. In addition, high-quality images can be formed even with an apparatus having a simple structure, and various types of inks can be used for printing; thus, ink jet printing systems have been increasingly used in a wide range of fields.
In particular, ink jet recording inks have come into significantly wide use by general consumers; among such inks, aqueous inks that are excellent in terms of nature conservation and environmental protection and that exhibit high safety in use are used. Since the fastness of printed articles, such as weather (light) resistance and water resistance, is considered important, pigments have come to be used as colorants.
Aqueous inks produced with pigments of three primary colors of Y, M, and C, however, exhibit a narrow color reproduction range as compared with aqueous inks containing dyes, which is problematic. There has been an approach to overcoming this problem, in which red (R), green (G), blue (B), orange (O), and violet (V) inks (inks of extra colors) containing colorants having different hues from the three primary colors are additionally used to enlarge a color reproduction range. This approach involves use of a red ink that is an aqueous ink containing C. I. Pigment Red 254 as a pigment and use of an ink set including such a red ink (Patent Literature 1).
C. I. Pigment Red 254 itself, however, has poor dispersibility on media which need to be colored; in addition to such poor dispersibility, C. I. Pigment Red 254 is less likely to exhibit good storage stability, such as no hue change or little change in a dispersed particle size, at high temperature for a long period especially when dispersed in water. These properties are problematic.